Various forms of adjustable wrenches are well known. One is the so called “Monkey Wrench”, in which there are two separate jaws, like scissors, which can be swung together by means of operating two handles. Another form is a wrench in which there is one fixed jaw and in which there is an adjustable jaw operated by means of a screw threaded rod, and a knurled nut. Numerous other forms of adjustable wrenches have been proposed.
The monkey wrench type of adjustment suffers from the problem that while it provides a firm grip on the nut, it can easily damage the nut so that it can not be reused. The form of wrench in which the adjustment is achieved by a threaded rod and a nut, is usually unsatisfactory. It is difficult to adjust the wrench to exactly the right opening, and it is common that the adjustment does not remain fixed, and the wrench may end up damaging the nut.
One of the fundamental problems with adjustable wrenches is that the two jaws of the wrench should be maintained exactly parallel to one another, in order to grasp the opposite flat surfaces on a nut. However, this is seldom the case. Usually one jaw will move and result in a poor fit on the nut.